This application claims the benefit of and priority from Japanese Applications No. 2000-171579 filed Jun. 8, 2000 and No. 2001-11652 filed Jan. 19, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel cutoff valve mounted on a fuel tank. More particularly, the invention relates to fuel cutoff valves for use in automobiles.
2.Description of Related Art
A conventional fuel cutoff valve is described in JPA 6-297968. In FIG. 14, which shows a conventional fuel valve, a fuel cutoff valve 200 comprises a full fuel control valve that shuts off when the full fuel level is exceeded, and an overfill prevention valve that shuts off when the fuel is fed past the full fuel level, and the overfill level is exceeded. Specifically, the fuel cutoff valve 200 comprises a casing 202 mounted on a fuel tank (not shown), a first float valve 210 housed in the casing 202, a spring 219 for urging the first float valve 210, and a second float valve 220 housed in the first float valve 210. The upper end of the casing 202 is provided with a wall 204. A connection hole 204a connected to a fuel vapor exhaust pipe 206 is formed in the center of the wall 204. A retainer 208 is mounted on the lower end of the casing 202.
The first float valve 210 comprises a thick-walled cylindrical lower portion 212, an upper portion 214 configured as an upwardly extending thick-walled cylinder whose lower end is mounted around the upper end portion of the lower portion 212, a cover plate 216 for covering the upper opening of the upper portion 214, and a valve box 218 interposed in an airtight manner between the outer circumference of the lower end of the cover plate 216 and the upper end of the upper portion 214. The first float valve 210 is supported by the spring 219 on the lower portion 212. The center of the cover plate 216 is provided with a projection 216a. The projection 216a is disposed facing the connection hole 204a and can be attached to the connection hole 204a or detached therefrom. The projection 216a is provided with a connection hole 216b, which is coaxially aligned with the connection hole 204a. A vent 214a is provided above the wall surrounding the upper portion 214, and the interior of the upper portion 214 is normally connected to the vapor phase of the fuel tank through the vent 214a and a vent 202a provided to the casing 202. The bottom of the valve box 218 is provided with a connection hole 218a. 
The second float valve 220 is disposed inside the upper portion 214. The second float valve 220 is supported by a spring 222 on the upper end face of the lower portion 212 of the first float valve 210, and the upper end thereof is provided with a projection 220a in a facing arrangement with the connection hole 218a. The valve box 218 also houses a relief valve 230. The relief valve 230 is designed to open and close the connection hole 218a by the urging of a valve body 232 with a spring 234.
The operation of the fuel cutoff valve 200 will now be described. The first float valve 210 alone experiences buoyancy when the liquid level inside the tank is in the vicinity of the full fuel liquid level. The first float valve 210 moves up and blocks the connection hole 204a with the projection 216a on the upper end thereof. In the process, the second float valve 220 moves together with the first float valve 210, but the projection 220a leaves the connection hole 218a open because of the absence of mutual displacement between the second float valve 220 and the first float valve 210.
In this state, the relief valve 230 closes the connection hole 218a, so the fuel vapor exhaust pipe 206 is blocked by the mutual engagement of the connection hole 204a and the projection 216a. The relief valve 230 opens when the pressure inside the tank exceeds a predetermined level. The gas inside the tank thus escapes from the fuel vapor exhaust pipe 206 via the vent 202a, vent 214a, connection hole 218a, connection hole 216b, and connection hole 204a, and the inside pressure is kept below a predetermined level.
If the liquid level inside the tank rises in an abnormal manner and the second float valve 220 is also buoyed, the second float valve 220 rises relative to the first float valve 210, blocking the connection hole 218a. The fuel cutoff valve 200 thus operates such that the interior of the fuel tank is separated from the outside by the second float valve 220 when the liquid level exceeds the full fuel liquid level, which is a level at which the first float valve 210 operates as a closing device.
In the fuel cutoff valve 200, the connection hole 204a is a narrow conduit incapable of rapidly removing fuel vapors into the canister from the fuel tank when a large amount of fuel is supplied. However, increasing the surface area of the conduit formed by the connection hole 204a increases the seal diameter and presses the first float valve 210 with greater force against the sealing surface facing the connection hole 204a. A resulting shortcoming is that the first float valve 210 does not open as readily, that is, valve reopening characteristics are adversely affected, when the liquid level of the fuel tank drops below a prescribed value. Techniques in which the floats are provided in two stages have been proposed as a means to overcome this shortcoming, as have been structures in which the full fuel control valve and the overfill prevention valve are provided at separate locations, but these structures are too complicated and make vehicles harder to assemble.
An aspect of the present invention is to provide a fuel cutoff valve that is capable of preventing overfilling, possesses improved valve reopening characteristics, and has a simple structure.
The present invention provides a fuel cutoff valve mounted on a fuel tank and is designed to connect the interior of the fuel tank with the outside or to separate the tank from the outside. The fuel cutoff valve is characterized by a casing including a casing main body partially extending into the upper portion of the fuel tank and having a first valve chamber, an outer conduit disposed outside the fuel tank, a first connection conduit designed to connect the outer conduit and the first valve chamber and configured such that the conduit surface area thereof is at least ⅓ that of the outer conduit, and a first seat disposed on the side of the first valve chamber facing the first connection conduit. A first float including a first float main body is disposed inside the first valve chamber and is capable of moving up and down. A first valve element opens and closes the first connection conduit by attaching itself to and detaching itself from the first seat provided to the upper portion of the first float main body. A storage chamber is formed in the axial center of the first float main body and is designed to form a connection with the first valve chamber. A second connection conduit is disposed in the upper portion of the first float main body and is designed to connect together the first connection conduit and the storage chamber and provided with a smaller conduit surface area than the first connection conduit. A second float including a second float main body is disposed in the storage chamber and is capable of moving up and down. A second valve element is disposed in the upper portion of the second float main body and is designed to open and close the second connection conduit. The first float is configured such that the first connection conduit is closed by the first valve element as a result of a rising movement when the fuel level in the fuel tank exceeds a first liquid level. The second float is configured such that the second connection conduit is closed by the second valve element as a result of a rising movement when the fuel level exceeds a second liquid level located above the first liquid level. The storage chamber is connected to the first connection conduit through the second connection conduit to reduce the force with which the first valve element is pressed against the first seat as a result of the fact that the fuel level has dropped below the second liquid level but is still above the first liquid level.
In the fuel cutoff valve pertaining to the present invention, the interior of the fuel tank is connected to the outside through the first valve chamber, first connection conduit, and outer conduit when the fuel level inside the fuel tank does not exceed the first liquid level. The first connection conduit is not constricted by the outer conduit, which is shaped such that the connection conduit surface area is at least ⅓ of the outer conduit surface area, allowing the fuel vapors in the fuel tank to rapidly escape outside.
The first float rises when the fuel level in the fuel tank exceeds the first liquid level as a result of refueling, whereby the first valve element is pressed against the first seat, the first connection conduit is closed, and the liquid fuel is prevented from flowing outside. At this time, the second connection conduit remains open, and the interior of the fuel tank is connected to the outside. When the liquid fuel rises further and exceeds a second liquid level which is above the first liquid level, the second float rises, the second valve element is pressed against a second seat, and the second connection conduit is closed. Thus, supplying fuel until the second liquid level is exceeded will raise the pressure inside the fuel tank and will trigger the fuel cutoff valve into stopping the supply of fuel.
As the fuel is consumed and the fuel level drops below the second liquid level, the second valve element is pushed away from the second seat, and the second connection conduit is opened by the descending second float. The storage chamber is thereby connected to the first connection conduit, and the pressure difference for the first connection conduit is reduced to zero. The absence of pressure difference is equivalent to reducing the force with which the first valve element is pressed against the first seat, allowing the first valve element to move smoothly away from the first seat.
Thus, the second float has a valve-closing function for closing the conduit at the second liquid level, and a valve reopening function for facilitating the reopening of the channel by the first float. In addition, the second float is disposed inside a storage chamber formed in the axial center of the first float, making it possible to implement these two functions in a compact structure.
According to a preferred embodiment, the first float has a cylindrical portion that extends from the lower end of the first float to a point below the lower end of the casing, the space inside the cylindrical portion constitutes part of the storage chamber, and the lower portion of the second float is disposed partially in the storage chamber. The second float can thus be elongated and housed in the storage chamber of the cylindrical portion. The outside diameter of the second float can be reduced, and the float itself can be compactly configured.
According to another preferred embodiment, the first float has a lower cover oriented substantially horizontally and disposed somewhat above the lower end of the first float such that the lower cover partitions off the lower side of the storage chamber.
With this structure, the second float is configured such that after the lower portion of the first float is immersed in fuel, the fuel enters the storage chamber and the buoyancy chamber, and buoyancy is created. Specifically, raising the liquid level above that of the first float is the factor that allows the second float to become buoyant, making it possible to move the start of level increase closer to the second liquid level and to facilitate setting the level at which the conduit is securely closed once the second liquid level is exceeded.
According to a preferred embodiment of the lower cover, the amount of fuel entering the buoyancy chamber can be reduced by adopting a structure in which a cylindrical projection extends toward the buoyancy chamber and has a smaller volume than the buoyancy chamber. Rapid discharge can therefore be achieved and the second float can descend unimpeded when the fuel enters the buoyancy chamber as a result of the rising fuel level.
Another feature of the first float is that connection holes for reducing the lift of the second float by reducing the negative pressure and the flow of air through the storage chamber can be provided at a plurality of locations in the vertical direction of the first float.
In the first float thus configured, the air flowing toward the storage chamber and the second connection conduit via side connection holes can be slowed down by providing the float upper body with side connection holes connected to the storage chamber. The negative pressure in the upper portion of the storage chamber can be reduced by the formation of a connection hole in the upper portion of the float lower body, making it possible to reduce the force that moves the second float upward.
Consequently, the second float can be accurately lifted at a position in which the second liquid level is exceeded because of a reduction in the lifting force acting on the air flowing through the storage chamber. That is, a reduction in the lifting force existing before the fuel level exceeds the second liquid level.
The wide first connection conduit can be provided with a tight seal by forming the first valve element from a plate-shaped seat material.
The casing comprises a third connection conduit for connecting the interior of the fuel tank to the outside, and a relief valve for opening the third connection conduit when the pressure inside the fuel tank rises above a predetermined level. This arrangement allows the pressure inside the fuel tank to be kept below a predetermined level.
According to another preferred embodiment, the fuel cutoff valve comprises a third float disposed in a facing arrangement with the relief valve and designed to close the third connection conduit when a third liquid level, which is located above the second liquid level, is exceeded. With this arrangement, fuel is prevented from escaping outside when the vehicle vibrates, tilts, or the like.
According to a preferred embodiment of the third float, the third connection conduit is disposed eccentrically in relation to the central axis of the first valve chamber, the third float is disposed above the first float inside the first valve chamber and is provided with substantially the same diameter as the first float, and a third valve element is placed in a facing arrangement with the third connection conduit. The third float should preferably be rendered nonrotatable relative to the casing to prevent the third valve element from changing its position.